1. Flow of study selection and descriptives
- 1.1 Description of experiment types and methodological approach
2. TAAR1 Agonists v Control
3 TAAR1 Agonist v known antipsychotic drug
4 Co-treatment with TAAR1 agonist plus known antipsychotic drug v known antipsychotic drug alone
5 Effect of TAAR1 agonists in TAAR1 receptor knockout animals
6. Proportion of animals not progressing to outcome measurement, potentially reflecting adverse effects of treatment
7. Summary of the evidence
8. Software used

1. Flow of study selection and descriptives

The flow of study selection is shown in Figure 1. Studies included were published between 2011 and 2024. Overall, this analysis includes 23 studies containing 392 comparisons.

Figure 1 - PRISMA flowchart

The table below gives a summary of the included studies, the model and species used, the intervention tested, and the outcome measured. N represents an aggregate of animals contributing to outcomes reported from control and treatment groups, and if the same control group has contributed to more than one experiment, it will be counted twice.

Study	Model	Strain	Comparison	Outcome	TAAR1 Receptor Status	N
Studies in previous review						3289*
BEGNI, 2021	Pharmacological	Lister hooded (rat)	SEP-363856 v Vehicle	Cognition	WT	40
				Locomotor activity	WT	120
CINQUE, 2018	Genetic	Wistar (rat)	RO5203648 v Vehicle	Cognition	WT	32
DEDIC, 2019	Pharmacological	C57BL/6J (mouse)	SEP-363856 v Vehicle	Locomotor activity	WT	48
			SEP-363856 v clozapine	Locomotor activity	WT	48
		Sprague-dawley (rat)	SEP-363856 v Vehicle	Locomotor activity	WT	18
				Social interaction	WT	48
			SEP-363856 v clozapine	Social interaction	WT	48
GALLEY, 2012	Pharmacological	Wistar (rat)	RO5073012 v Vehicle	Locomotor activity	WT	48
KOKKINOU, 2021	Pharmacological	C57BL/6 (mouse)	SEP-363856 v Vehicle	Neurobiological outcome	WT	17
KRASAVIN, 2022a	Genetic	Wistar (rat)	LK000764 v Vehicle	Locomotor activity	WT	108
	Pharmacological	Wistar (rat)	LK000764 v Vehicle	Locomotor activity	WT	140
KRASAVIN, 2022b	Genetic	Wistar (rat)	AP163 v Vehicle	Locomotor activity	WT	18
LEO, 2018	Genetic	Wistar (rat)	RO5203648 v Vehicle	Locomotor activity	WT	24
LIANG, 2022	Pharmacological	ICR (mouse)	SEP-363856 & olanzapine v olanzapine	Cognition	WT	48
				Locomotor activity	WT	16
			SEP-363856 v Vehicle	Cognition	WT	192
				Locomotor activity	WT	96
			SEP-363856 v olanzapine	Cognition	WT	48
				Locomotor activity	WT	16
REVEL, 2011	Genetic	C57BL/6J (mouse)	RO5166017 v Vehicle	Locomotor activity	WT	42
	Pharmacological	C57BL/6 (mouse)	RO5166017 v Vehicle	Locomotor activity	WT	148
					TAAR1 R KO	52
			RO5166017 v Vehicle	Stereotypy	WT	88
					TAAR1 R KO	40
		NMRI (mouse)	RO5166017 v Vehicle	Locomotor activity	WT	84
REVEL, 2012a	Genetic	C57Bl/6Jx129Sv/J (mouse)	RO5203648 v Vehicle	Locomotor activity	WT	48
	Pharmacological	C57BL/6J (mouse)	RO5203648 v Vehicle	Locomotor activity	WT	154
		Wistar (rat)	RO5203648 v Vehicle	Locomotor activity	WT	84
REVEL, 2012b	Pharmacological	C57BL/6J (mouse)	RO5073012 v Vehicle	Locomotor activity	WT	42
REVEL, 2013	Pharmacological	C57BL/6J (mouse)	RO5256390 v Vehicle	Locomotor activity	WT	122
			RO5256390 v olanzapine	Locomotor activity	WT	32
			RO5263397 & risperidone v risperidone	Locomotor activity	WT	96
			RO5263397 v Vehicle	Locomotor activity	WT	184
			RO5263397 v olanzapine	Locomotor activity	WT	80
			RO5263397 v risperidone	Locomotor activity	WT	96
		Long-evans (rat)	RO5256390 v Vehicle	Cognition	WT	48
		NMRI (mouse)	RO5256390 v Vehicle	Locomotor activity	WT	80
			RO5263397 v Vehicle	Locomotor activity	WT	128
SAARINEN, 2022	Pharmacological	C57Bl/6J (mouse)	SEP-363856 v Vehicle	Locomotor activity	WT	56
					TAAR1 R KO	48
			SEP-363856 v Vehicle	Prepulse inhibition	WT	60
					TAAR1 R KO	60
WANG, 2023	Pharmacological	C57BL/6J (mouse)	Compound 50A v Vehicle	Locomotor activity	WT	72
			Compound 50B v Vehicle	Locomotor activity	WT	90
			Compound 50B v aripiprazole	Locomotor activity	WT	16
			Compound 50B v risperidone	Locomotor activity	WT	16
			SEP-363856 v Vehicle	Locomotor activity	WT	18
			SEP-363856 v aripiprazole	Locomotor activity	WT	16
			SEP-363856 v risperidone	Locomotor activity	WT	16
New studies added in this iteration						3629*
CICHERO, 2023	Genetic	Wistar (rat)	Guanfacine v Vehicle	Locomotor activity	WT	20
COTTER, 2015	Pharmacological	Long-evans (rat)	RO5203648 v Vehicle	Locomotor activity	WT	40
ESPINOZA, 2018	Genetic	C57Bl/6Jx129Sv/J (mouse)	RO5263397 v Vehicle	Locomotor activity	WT	48
LI, 2024	Pharmacological	Not stated (mouse)	SEP-363856 v Vehicle	Cognition	WT	240
				Locomotor activity	WT	180
				Prepulse inhibition	WT	180
				Social interaction	WT	60
				Stereotypy	WT	60
			SEP-363856 v olanzapine	Cognition	WT	216
				Locomotor activity	WT	162
				Prepulse inhibition	WT	162
				Social interaction	WT	54
				Stereotypy	WT	54
SHANG, 2023	Pharmacological	C57BL/6J (mouse)	SEP-363856 v Vehicle	Cognition	WT	24
				Locomotor activity	WT	141
					TAAR1 R KO	13
				Prepulse inhibition	WT	285
			ZH8651 v Vehicle	Cognition	WT	24
				Locomotor activity	WT	111
					TAAR1 R KO	20
				Prepulse inhibition	WT	270
					TAAR1 R KO	60
			ZH8659 v Vehicle	Cognition	WT	24
				Locomotor activity	WT	111
					TAAR1 R KO	20
				Prepulse inhibition	WT	270
					TAAR1 R KO	57
			ZH8667 v Vehicle	Locomotor activity	WT	19
THORN, 2014	Pharmacological	Sprague-dawley (rat)	RO5263397 v Vehicle	Locomotor activity	WT	180
YUN, 2023	Pharmacological	C57BL/6J (mouse)	SEP-363856 v Vehicle	Locomotor activity	WT	176
				Prepulse inhibition	WT	28
ZHOU, 2024	Pharmacological	C57BL/6J (mouse)	Compound 6e v Vehicle	Cognition	WT	20
				Locomotor activity	WT	60
			Compound 7b v Vehicle	Cognition	WT	20
				Locomotor activity	WT	60
			Compound 8b v Vehicle	Cognition	WT	20
				Locomotor activity	WT	60
			SEP-363856 v Vehicle	Cognition	WT	20
				Locomotor activity	WT	60

References of included studies are located in the appendix. Included studies used 49 unique disease model induction procedures.*some animals contributed to more than one experimental outcome; this number reflects the number of outcomes rather than the number of animals.

1.1 Description of experiment types and methodological approach

Within the literature we identified distinct categories of experiments and the data presented would allow several meta-analytical contrasts to be drawn:

TAAR1 agonist vs control. These were experiments investigating the effect of administering a TAAR1 agonist alone, reported in 281 experiments from 23 publications.
TAAR1 agonist vs ‘known’ antipsychotic drug. These were experiments investigating the effect of administering a TAAR1 agonist alongside a currently licensed anti-psychotic reported in 51 experiments from 5 publications.
Co-treatment with TAAR1 agonist plus know antipsychotic drug v known antipsychotic drug alone, reported in 10 experiments from 2 publications.
Effect of TAAR1 receptor knock-out on the effect of TAAR1 agonist v control. These were experiments investigating whether any effect of TAAR1 agonism was inhibited by TAAR1 antagonism. In this iteration of the review, all experiments within this category used genetic approaches to TAAR1 antogonism (that is, they knocked out the gene for the TAAR1 receptor, so any observed drug effect could not be due to actions mediated through the TAAR1 receptor, and therefore could not be considered specific drug effects mediated through the TAAR1 receptor). This was the case for 20 experiments from 3 publications.

Each experiment type is analysed separately. This is because each experiment type uses different control conditions.

In these studies the:

Control group is a group of animals that is (1) subjected to a psychosis model induction paradigm and (2) administered a control treatment (vehicle) or no treatment
Intervention group is a group of animals that is (1) subjected to a psychosis model induction paradigm and (2) administered a TAAR1 agonist treatment
Sham group is a group of animals that is (1) not subjected to a psychosis model induction paradigm and (2) administered a control treatment (vehicle) or no treatment. These data are required to allow a ‘normalised mean difference’ (NMD) effect size to be calculated, given by

\[ \frac{(\text{$\bar{\mu}_C - \bar{\mu}_T$})} {(\text{$\bar{\mu}_C - \bar{\mu}_S$)}} \text{ x 100} \]

where $\bar{\mu}_C$, $\bar{\mu}_T$, $\bar{\mu}_S$ are the mean reported scores in the control, treatment, and sham groups respectively.

Outcomes with ≥2 independent effect sizes were considered for meta-analysis. In this iteration of the review, this includes locomotor activity, cognition, prepulse inhibition, social interaction and stereotypy.

All analyses were conducted allowing for the following hierarchical levels in a random effects model, which accounts for features common to experimental contrasts such as a shared control group:

Level 1: Rodent strain - effect sizes measured across experiments using the same rodent strain
Level 2: Study - effect sizes measured from different experiments presented in the same publication
Level 3: Experiment - effect sizes measured in the same experiment within a study, where often a control group contributes to several effect sizes

The hierarchical grouping may therefore be considered thus: Strains of laboratory animals are included in several Studies, each of which can report one or more Experiments, and each Experiment is comprised of at least two Cohorts which are considered identical except for differing in the experimental manipulation (the Intervention) or not being exposed to the disease modelling procedures (a Sham cohort, these only being used to provide a baseline for outcome measures to allow Normalised Mean Difference meta-analysis). An Experiment can include several experimental contrasts, for instance where different doses of drugs are compared to the same control group.

For some experimental contrasts, more than one locomotor or cognitive outcome - for instance both horizontal and vertical climbing activity - was measured in the same cohort of animals. Further, some publications used the same drug doses with the same outcome measures in different experiments. For these reasons, some of the forest plots may appear to include ‘duplicate’ Study - Drug - Dose combinations with different outcomes. For the former there were insufficient levels of the different locomotor or cognitive outcome measures to allow for hierachical analysis and so this was not performed; and for the later, these are accounted for in the heirarchical analysis.

2. TAAR1 Agonists v Control

23 studies (281 comparisons) investigated the effects of TAAR1 Agonist versus Control. The number of studies and individual effect sizes for each outcome were:

Locomotor activity*: 21 studies and 188 comparisons in 11 strains
Pre pulse inhibition*: 4 studies and 46 comparisons in 3 strains
Cognitive function: 7 studies and 34 comparisons in 6 strains
Social interaction: 2 studies and 5 comparisons in 2 strains
Stereotypy: 2 studies and 7 comparisons in 2 strains

* These outcomes were identified in the study protocol as primary outcomes of interest.

Since only two publications reported each of social interaction and stereotypy, these outcomes are not analysed further.

2.1 Outcome 1: Locomotor Activity

2.1.1 Risks of bias

Figure 2.1.1 shows the risk of bias summary for studies investigating the effect of administering a TAAR1 agonist on locomotor activity in animals. The risk of bias assessment was performed using the SyRCLE’s RoB tool.

Figure 2.1.1 - Traffic light plot of the risk of bias for locomotor activity

2.1.2 Reporting completeness

Figure 2.1.2 shows the reporting completeness summary for studies investigating the effect of administering a TAAR1 agonist on locomotor activity in animals. The reporting completeness assessment was performed using the ARRIVE guidelines. Studies which did not report are labelled ‘High’, those which did report are labelled ‘Low’.

Figure 2.1.2 - Traffic light plot of the reporting completeness for locomotor activity

2.1.3 Meta-analysis

The effect of administering a TAAR1 agonist on locomotor activity in animals using SMD as the effect size is shown in Figure 2.1.3. The pooled estimate for SMD across all individual comparisons is displayed as a diamond shape at the bottom of the plot. Dotted lines indicate the prediction interval of the pooled estimate.

Figure 2.1.3 - Forest plot of locomotor activity for TAAR1 Agonist vs control

For TAAR1 Agonist v Control, TAAR1 interventions had a pooled effect on locomotor activity of SMD = 1.109 (95% CI: 0.837 to 1.38, with a prediction interval of -0.507 to 2.724).

188 experimental comparisons were reported in 60 experiments reported from 21 publications and involving 11 different animal strains.

The following table structure is used throughout this report and is used to show the different levels contributing to that analysis, the number of unique categories in those levels, and the variance contributed by that level of analysis. Because levels are only included in the analysis where there are five or more unique categories, for some analyses the number of categories is 0, and the variance attributed to those levels in not applicable. Because the model is hierarchical, where for instance there are Studies which include different Strains, the number of categories for Study x Strain will exceed the number of Studies (or publications) referred to in the text.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0
Study x Strain	27	0.066
Study x Strain x Experiment	60	0.445

2.1.4 Subgroup analyses and meta-regressions

For each outcome, the covariates of interest for subgroup analyses and meta-regressions were:

Sex
Method of disease induction
Route of intervention administration
Whether the intervention was prophylactic or therapeutic (i.e. administered before or after disease model induction)
Duration of treatment period
The intervention administered
The efficacy of the drug (i.e. whether the drug is a partial or full agonist)
The selectivity of the drug
Potency of the intervention
Dose of intervention

We also conducted subgroup analyses using (1) SyRCLE Risk of Bias and (2) ARRIVE reporting completeness assessment scores as covariates to evaluate their influence on effect size estimates. These were not specified in the study protocol, but evaluation of risk of bias is required for the Summary of Evidence table, and no studies were considered at low risk of bias or high reporting completeness to allow such a sensitivity analysis

Only 21% of studies overall reported either a mean age, or an age range, of the experimental animals, so this was not analysed further.

The significance (p value) reported is that for a test of whether the moderators are significantly different one from another, rather than whether the effect is significantly different from 0.

Sex

Figure 2.1.4.1 displays the estimates for the pooled SMD’s when comparisons are stratified by sex of the animal. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.1.4.1 - Subgroup analysis of TAAR1 agonist vs control on locomotor activity by sex

The p-value for the association between the sex of animal groups used and outcome reported was 0.239.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0
Study x Strain	27	0
Study x Strain x Experiment	60	0.501

Category of disease induction

Figure 2.1.4.2 displays the estimates for the pooled SMD’s when comparisons are stratified by the category of disease induction. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.1.4.2 - Subgroup analysis of TAAR1 agonist vs control on locomotor activity by category of disease induction

The p-value for the association between whether genetic or pharmacological models were used and outcome reported was 0.547.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0
Study x Strain	27	0.075
Study x Strain x Experiment	60	0.444

Disease model induction

Figure 2.1.4.3 displays the estimates for the pooled SMDs for experiments using pharmacological model inductions, stratified by the drug used to induce the model. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD for pharmacological induction models is displayed as an elongated diamond shape at the bottom of the plot, and summary data grouping drugs as ‘Stimulants or dopamine agonists’ or ‘NMDA antagonists’ is shown with diamond symbols and in bold text. This analysis was not pre-specified in the study protocol for the first iteration of this review, but was suggested in peer review of that protocol. The summary estimate differs slightly from that in Fig 2.1.4.2, likely because we generated a different variance-covariance matrix.

Figure 2.1.4.3 - Subgroup analysis of TAAR1 agonist vs control on locomotor activity by pharmacological category of disease induction

The p-value for the association between different categories of pharmacological induction (‘Stimulants or dopamine agonists’ versus ‘NMDA antagonists’) and outcome reported was = 0.03.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	10	0
Study x Strain	21	0.076
Study x Strain x Experiment	53	0.485

Route of intervention administration

Figure 2.1.4.4 displays the estimates for the pooled SMD’s when comparisons are stratified by the route of intervention administration. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.1.4.4 - Subgroup analysis of TAAR1 agonist vs control on locomotor activity by route of intervention administration

The p-value for the association between the route of intervention administration and outcome reported was 0.1.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0.066
Study x Strain	27	0
Study x Strain x Experiment	60	0.44

Prophylactic or therapeutic intervention

Figure 2.1.4.5 displays the estimates for the pooled SMD’s when comparisons are stratified by whether the intervention was administered prophylactically or therapeutically. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot. This categorisation is co-linear with that for route of administration - all treatments given after the induction of locomotor activity were given intraperitoneally.

Figure 2.1.4.5 - Subgroup analysis of TAAR1 agonist vs control on locomotor activity by intervention type

The p-value for the association between whether the intervention was administered prophylactically or therapeutically and outcome reported was 0.704.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0
Study x Strain	27	0.064
Study x Strain x Experiment	60	0.461

Duration of treatment period

In this iteration of the review, all relevant comparisons administered the TAAR1 agonist for < 1 week. Therefore, no subgroup analyses were conducted for this variable.

The intervention administered

Figure 2.1.4.7 displays the estimates for the pooled SMD’s when comparisons are stratified by the intervention administered. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.1.4.7 - Subgroup analysis of TAAR1 agonist vs control on locomotor activity by intervention administered

The p-value for the association between the intervention and outcome reported was 0.565.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0
Study x Strain	27	0.113
Study x Strain x Experiment	60	0.489

The efficacy of the drug (i.e. whether the drug is a partial or full agonist)

Figure 2.1.4.8 displays the estimates for the pooled SMD’s when comparisons are stratified by the action/efficacy of the intervention administered. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.1.4.8 - Subgroup analysis of TAAR1 agonist vs control on locomotor activity by efficacy of the drug

The p-value for the association between whether the drug was a full or partial agonist and outcome reported was 0.34.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0
Study x Strain	27	0.074
Study x Strain x Experiment	60	0.444

The selectivity of the drug

Figure 2.1.4.9 displays the estimates for the pooled SMD’s when comparisons are stratified by the selectivity of the intervention administered. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.1.4.9 - Subgroup analysis of TAAR1 agonist vs control on locomotor activity by selectivity of the drug

The p-value for the association between whether the drug was highly selective, or also manifests 5-HT1A (“5HT1A part. ag”) or $/a$-2 adrenergic (“Adr a2 ag”) effects, and outcome reported was 0.621.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0
Study x Strain	27	0.076
Study x Strain x Experiment	60	0.444

Potency of intervention

The pEC50 value of each drug was used to measure potency. The pEC50 value is the negative logarithm (to base 10) of the EC50 value. Higher pEC50 values indicate higher potency (as they indicate a lower EC50). Figure 2.1.4.10 displays a visualisation of the meta-regression using the pEC50 value as an explanatory variable. Dashed lines represent the 95% confidence interval of the regression line. The dotted lines represent the 95% prediction interval. Raw data are plotted with ‘bubble’ size adjusted according to effect size precision.

Figure 2.1.4.10 - Meta-regression of TAAR1 agonist vs control on locomotor activity by potency of intervention

The estimate for $\beta$ was -0.166 (p = 0.14).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0
Study x Strain	27	0.083
Study x Strain x Experiment	60	0.453

Dose of intervention

In this iteration of the review, the TAAR1 agonists tested against control for their effect on locomotor activity were: SEP-363856, RO5263397, RO5203648, RO5166017, LK000764, RO5256390, Compound 50B, ZH8651, ZH8659, Compound 50A, RO5073012, AP163, Compound 6e, Compound 7b, Compound 8b, Guanfacine and ZH8667. Meta-analysis was conducted where data were available from more than nine experiments in more than two publications. The dashed lines in the plot represent the 95% confidence interval of the regression line and the dotted lines represent the 95% prediction interval. Raw data are plotted with point size adjusted according to effect size precision.

RO5263397: There were 36 comparisons from 3 publication(s).

The estimate for $\beta$ was 0.159 (p = 0.003).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	4	0
Study x Strain	4	0
Study x Strain x Experiment	11	0.831

RO5203648: There were 25 comparisons from 3 publication(s).

The estimate for $\beta$ was 0.028 (p = 0.119).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	4	0
Study x Strain	5	0
Study x Strain x Experiment	9	0.567

SEP-363856 (Ultaront): There were 41 comparisons from 9 publication(s).

The estimate for $\beta$ was 0.054 (p = 0.002).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0
Study x Strain	10	0.493
Study x Strain x Experiment	20	0.421

RO5166017: There were 18 comparisons from 1 publication(s).

LK000764: There were 16 comparisons from 1 publication(s).

RO5256390: There were 14 comparisons from 1 publication(s).

Compound 50B: There were 5 comparisons from 1 publication(s).

ZH8651: There were 5 comparisons from 1 publication(s).

ZH8659: There were 5 comparisons from 1 publication(s).

Compound 50A: There were 4 comparisons from 1 publication(s).

RO5073012: There were 4 comparisons from 2 publication(s).

Compound 8b: There were 3 comparisons from 1 publication(s).

Compound 6e: There were 3 comparisons from 1 publication(s).

Compound 7b: There were 3 comparisons from 1 publication(s).

AP163: There were 3 comparisons from 1 publication(s).

Guanfacine: There were 2 comparisons from 1 publication(s).

ZH8667: There were 1 comparisons from 1 publication(s).

Standardised dose

We then sought evidence of a dose response relationship across all drugs. To do this, we conducted meta-regression using a constructed variable, the ‘standardised dose’. The EC50 of a drug is the molar concentration at which 50% of the maximal response occurs. While the drug concentrations achieved at the receptor are unknown, we can approximate this from the dose given (expressed as g/kg), and the molar mass of the drug (g/mol). This relies on an approximation that the drug is equally distributed throughout the animal, and so does not take into account for example first pass metabolism for orally administered drugs, blood brain barrier solubility or differential accumulation in fatty tissues. As such, it should be interpreted with extreme caution; but does provide allow some imputation of whether, across all drugs, there is a dose-response effect. On this measure, a standardised dose of 0 would reflect 50% of maximum effect and a standardised dose of 1 would reflect around 80% of maximum effect

The standardised dose was calculated as the logarithm of the dose of the intervention (in g/kg) divided by the product of the intervention’s EC50 (in moles) and the Molar mass of the drug (in g/mol):

\[ \log\frac{(\text{Dose of Intervention (g/kg)})}{(\text{Molar Mass (g/mol)}) \times ({\text{EC50 (mol/l)}})} \]

This is a simplified approximation based on the reasoning that if drug actions are mediated through the TAAR1 receptor, and drug efficacy is reflected in the respective EC50 values, then in principal drugs should exhibit similar effects when acting at their respective EC50.

The actual concentration of a drug at the receptor site is influenced by several variables, including dosage, administration route, elimination half-life, and first-pass metabolism (in case of oral administration). Incorporating all these factors accurately would necessitate a detailed pharmacokinetic model, which falls outside the scope of this review. Here, we assume uniformity across experiments in terms of (i) volume of distribution, (ii) first-pass metabolism, (iii) blood-brain barrier permeability, and (iv) experimental design, especially regarding the timing of peak drug concentration (where we assume that experiments were designed to be done at a time when the drug was near peak concentration). We recognise the limitations of this approach, the findings of which should be interpreted with caution.

Figure 2.1.4.11 provides a visualisation of the meta-regression analysis relationship between standardised doses of TAAR1 agonists and the Standardized Mean Difference (SMD) change in Locomotor activity. As before, dashed lines represent the 95% confidence interval of the regression line and dotted lines represent the 95% prediction interval. Raw data are plotted with point size adjusted according to effect size precision.

Figure 2.1.4.11 - Meta regression of standardised dose for TAAR1 agonist vs control on locomotor activity

The estimate for the change in effect per log unit change in standardised dose was 0.414 (p < 0.001).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0.061
Study x Strain	27	0.149
Study x Strain x Experiment	60	0.488

SyRCLE RoB assessment considered as a categorical variable

Figure 2.1.4.12 displays the estimates for the pooled SMD’s when comparisons are stratified by how many of the SyRCLE risk of bias assessment criteria (of which there are 10) that the experiment met. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.1.4.12 - Subgroup analysis of TAAR1 agonist vs control on locomotor activity by SyRCLE RoB criteria met

The p-value for the association between SyRCLE Risks of Bias reporting and outcome reported was 0.006.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0.024
Study x Strain	27	0
Study x Strain x Experiment	60	0.373

SyRCLE RoB assessment considering those studies where any item is at low risk of bias

Figure 2.1.4.13 displays the estimates for the pooled SMD’s when comparisons are stratified by whether of not any of the SyRCLE Risk of bias domains were rated as low risk of bias. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.1.4.13 - Subgroup analysis of TAAR1 agonist vs control on locomotor activity by alternative SyRCLE RoB assessment

The p-value for the association between low SyRCLE Risks of Bias reporting and outcome reported was 0.795.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0
Study x Strain	27	0.079
Study x Strain x Experiment	60	0.447

ARRIVE reporting completeness guidelines

Figure 2.1.4.14 displays a visualisation of the meta-regression using the number of ARRIVE items met (from a possible total of 22) as an explanatory variable. Dashed lines represent the 95% confidence interval of the regression line. The dotted lines represent the 95% prediction interval. Raw data are plotted with ‘bubble’ size adjusted according to effect size precision.

Figure 2.1.4.14 - Meta-regression of number of ARRIVE items met for TAAR1 agonist vs control on locomotor activity

The estimate for $\beta$ was 0.023 (p = 0.667).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0
Study x Strain	27	0.076
Study x Strain x Experiment	60	0.448

Heterogeneity explained by covariates (TAAR1 Agonist vs Control on locomotor activity)

The table below summarises the heterogeneity observed for each covariate in the effect sizes of the effect of TAAR1 agonists on locomotor activity. We present marginal R² (the % change in the between-studies variance when the covariate is included in the model), which measures the proportion of variance explained by including moderators in the model . The coefficients are derived from an rma model fitted with an intercept (and so represent, for each category, the point estimate and 95% CIs of the effect in that category).

Moderator	Category	$\beta$	95% CI	Marginal R² (%)
Overall effect	-	1.109	0.837 to 1.38	-
Sex	-	-	-	7.9%
-	Female	0.94	0.028 to 1.851	-
-	Male	1.347	1.024 to 1.669	-
-	Mixed	0.705	0.148 to 1.262	-
-	Not reported	1.09	0.669 to 1.51	-
Category of disease model induction	-	-	-	1%
-	Genetic	1.298	0.619 to	-
-	Pharmacological	1.078	0.814 to 1.343	-
Pharmacological class of model induction	-	-	-	10.7%
-	NMDA antagonist	1.352	0.902 to	-
-	Stimulant or Dopamine agonist	0.812	0.38 to 1.243	-
Administration route	-	-	-	7.1%
-	Intraperitoneal	1.16	0.607 to 1.714	-
-	Oral	1.151	0.8 to 1.502	-
-	Subcutaneous	-0.062	-1.2 to 1.075	-
Prophylactic or therapeutic intervention	-	-	-	0.5%
-	Prophylactic	1.13	0.859 to 1.401	-
-	Therapeutic	0.991	0.296 to 1.686	-
Intervention administered	-	-	-	14.8%
-	AP163	1.371	-1.058 to 3.8	-
-	Compound 50A	0.604	-1.128 to 2.335	-
-	Compound 50B	1.05	0.079 to 2.021	-
-	Compound 6e	1.242	0.576 to 1.909	-
-	Compound 7b	0.697	0.042 to 1.353	-
-	Compound 8b	0.584	-0.071 to 1.239	-
-	Guanfacine	1.119	-1.061 to 3.3	-
-	LK000764	0.47	-0.999 to 1.938	-
-	RO5073012	0.68	-0.68 to 2.04	-
-	RO5166017	1.435	0.559 to 2.311
-	RO5203648	1.134	0.389 to 1.878	-
-	RO5256390	1.763	0.758 to 2.768	-
-	RO5263397	1.253	0.599 to 1.907	-
-	SEP-363856 (Ultaront)	1.004	0.572 to 1.436	-
-	ZH8651	1.054	0.462 to 1.646	-
-	ZH8659	1.113	0.52 to 1.706	-
-	ZH8667	0.41	-0.524 to 1.344	-
Drug efficacy	-	-	-	1%
-	Full agonist	1.166	0.892 to 1.441	-
-	Partial agonist	1.018	0.715 to 1.321	-
Drug selectivity	-	-	-	4.8%
-	High	1.249	0.896 to 1.602	-
-	Low - 5HT1A	0.965	0.596 to 1.334	-
-	Low - a2 Adr	1.119	-0.815 to 3.054
-	Unclear	0.888	0.479 to 1.298	-
Drug potency	per log unit	-0.166	-0.387 to 0.055	1.9%
Standardised drug dose	per log unit	0.414	0.317 to 0.511	22.2%
Risk of Bias	-	-	-	28.5%
-	0 criteria met	1.174	0.886 to 1.463	-
-	1 criteria met	0.534	0.01 to 1.058	-
-	2 criteria met	1.946	1.308 to 2.585	-
Reporting completeness	per log unit	0.023	-0.086 to 0.132	0.6%

2.1.5 Sensitivity Analyses

We examine the robustness of the findings for the primary outcome by performing the following sensitivity analyses

Imputed 𝞺 values of 0.2 and 0.8

In the previous analyses for the effect of TAAR1 agonists on locomotor activity, we imputed a $\rho$ value - the imputed within-study correlation between observed effect sizes - of 0.5. Here, we examine the effect of imputing $\rho$ values of 0.2 and 0.8.

When the $\rho$ value is assumed to be 0.2, the TAAR1 interventions had a larger effect on locomotor activity of SMD = 1.26 (95% CI: 0.9 to 1.62) with a prediction interval of -0.37 to 2.89).

When the $\rho$ value is assumed to be 0.8, the TAAR1 interventions had a smaller and more imprecise effect on locomotor activity of SMD = 0.82 (95% CI: 0.47 to 1.17) with a prediction interval of -1.42 to 3.06).

For reference the pooled effect size when rho is assumed to be 0.5 is 1.11 (95% CI: 0.84 to 1.38). Therefore, the effect is very sensitive to imputed within-study correlation between effect sizes.

Normalised Mean Difference (NMD)

For locomotor activity, 146 out of 188 comparisons, i.e. 77.7 % of comparisons, had data available for a Sham group and for these studies it was possible to calculate an NMD estimate of effect size.

The effect of administering a TAAR1 agonist on locomotor activity in animals using NMD as the effect size is shown in Figure 2.1.5. The pooled estimate for NMD across all individual comparisons is displayed as a diamond shape at the bottom of the plot. Dotted lines indicate the prediction interval of the pooled estimate.

Figure 2.1.5 - Forest plot of TAAR1 agonist vs control on locomotor activity using NMD

For TAAR1 Agonist v Control, TAAR1 interventions had a pooled effect on locomotor activity of NMD = 52.9 (95% CI: 37.5 to 68.4) with a prediction interval of -22.6 to 128.5). For reference the pooled effect size for SMD was 1.11 (95% CI: 0.84 to 1.38).

146 experimental comparisons were reported in 46 experiments reported from 17 publications and involving 11 different animal strains.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	219.3
Study x Strain	22	33.5
Study x Strain x Experiment	46	849.69

Robust variance estimator (RVE)

Here, we examine the robustness of results when using a sandwich-type estimator to obtain cluster-robust tests and confidence intervals of the model coefficients. The variance-covariance matrix is estimated using the ‘bias-reduced linearization’ for small-sample adjustment and Strain as a clustering variable.

When using the robust variance estimator, TAAR1 interventions had a pooled effect on locomotor activity of SMD = 1.11 (95% CI: 0.83 to 1.38 with a prediction interval of -0.89 to 3.11). For reference the pooled effect size for SMD was 1.11 (95% CI: 0.84 to 1.38), so the using a robust variance estimator does not substantially change the results.

2.1.6 Reporting bias/small-study effects

Because of the relationship between SMD effect sizes and variance inherent in their calculation, where study size is small the standard approach to seeking evidence of small-study effects (regression based tests including Egger’s regression test for multilevel meta-analysis) can lead to over-estimation of small-study effect (see for instance 10.7554/eLife.24260). To address this we used Egger’s regression test for multilevel meta-analysis, with regression of SMD effect size against 1/√N, where N is the total number of animals involved in an experiment.

Egger regression based on 188 effects of TAAR1 Agonist v Control where Locomotor activity was measured showed a coefficient for small-study effect of 7.29 (95% CI: 1.36 to 13.23; p = 0.017).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	11	0.06
Study x Strain	27	0.03
Study x Strain x Experiment	60	0.39

2.2 Outcome 2: Pre pulse inhibition

2.2.1 Risks of bias

Figure 2.2.1 shows the risk of bias summary for studies investigating the effect of administering a TAAR1 agonist on Pre pulse inhibition in animals. The risk of bias assessment was performed using the SyRCLE’s RoB tool.

Figure 2.2.1 - Traffic light plot of the risk of bias for Pre pulse inhibition

2.2.2 Reporting completeness

Figure 2.2.2 shows the reporting completeness summary for studies investigating the effect of administering a TAAR1 agonist on Pre pulse inhibition in animals. The reporting completeness assessment was performed using the ARRIVE guidelines. Studies which did not report are labelled ‘High’, those which did report are labelled ‘Low’.

Figure 2.2.2 - Traffic light plot of the reporting completeness for Pre pulse inhibition

2.2.3 Meta-analysis

The effect of administering a TAAR1 agonist on pre pulse inhibition in animals using SMD as the effect size is shown in Figure 2.2.3. The pooled estimate for SMD across all individual comparisons is displayed as a diamond shape at the bottom of the plot. Dotted lines indicate the prediction interval of the pooled estimate.

Figure 2.3.3 - Forest plot of effects on pre pulse inhibition for TAAR1 Agonist vs control

For TAAR1 Agonist v Control, TAAR1 interventions had a pooled effect on pre pulse inhibition of SMD =0.498 (95% CI: -0.051 to 1.048, with a prediction interval of -0.625 to 1.622).

46 experimental comparisons were reported in 6 experiments reported from 4 publications and involving 3 different animal strains.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	0	NA
Study x Strain	0	NA
Study x Strain x Experiment	6	0.15

2.2.4 Subgroup analyses and meta-regressions

Sex

Figure 2.2.4.1 displays the estimates for the pooled SMD’s when comparisons are stratified by sex of the animal. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.2.4.1 - Subgroup analysis of TAAR1 agonist vs control on Pre pulse inhibition by sex

The p-value for the association between the sex of animal groups used and outcome reported was = 0.172.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	0	NA
Study x Strain	0	NA
Study x Strain x Experiment	6	0.09

Category of disease induction

All studies used pharmacological models

Disease model induction

All but one study used NMDA antagonism as disease model induction

Route of intervention administration

Figure 2.2.4.3 displays the estimates for the pooled SMD’s when comparisons are stratified by the administration route of the intervention. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.2.4.3 - Subgroup analysis of TAAR1 agonist vs control on Pre pulse inhibition by route of intervention administration

The p-value for the association between whether genetic or pharmacological models were used and outcome reported was = 0.312.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	0	NA
Study x Strain	0	NA
Study x Strain x Experiment	6	0.1

Prophylactic or therapeutic intervention

In this iteration of the review, all relevant comparisons administered the TAAR1 agonist after induction of the disease model. Therefore, no subgroup analyses were conducted for this variable.

Duration of treatment period

In this iteration of the review, all relevant comparisons administered the TAAR1 agonist for < 1 week. Therefore, no subgroup analyses were conducted for this variable.

The intervention administered

Figure 2.2.4.4 displays the estimates for the pooled SMD’s when comparisons are stratified by the intervention administered. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.2.4.4 - Subgroup analysis of TAAR1 agonist vs control on Pre pulse inhibition by intervention administered

The p-value for the association between the intervention and outcome reported was < 0.001.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	0	NA
Study x Strain	0	NA
Study x Strain x Experiment	6	0.11

The efficacy of the drug (i.e. whether the drug is a partial or full agonist)

In this iteration of the review, all relevant comparisons administered the TAAR1 agonists with full TAAR1-Gs agonist activity (SEP-363856 and ZH8651) or which is a TAAR1-Gq agonist (ZH8659) Therefore, no subgroup analyses were conducted for this variable.

The selectivity of the drug

Figure 2.2.4.5 displays the estimates for the pooled SMD’s when comparisons are stratified by the selectivity of the intervention administered. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.2.4.5 - Subgroup analysis of TAAR1 agonist vs control on Pre pulse inhibition by selectivity of the drug

The p-value for the association between whether the drug was highly selective, or also manifests 5-HT1A effects, was = 0.027.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	0	NA
Study x Strain	0	NA
Study x Strain x Experiment	6	0.11

Potency of interventions

The pEC50 value of each drug was used to measure potency. The pEC50 value is the negative logarithm (to base 10) of the EC50 value. Higher pEC50 values indicate higher potency (as they indicate a lower EC50). Figure 2.2.4.6 displays a visualisation of the meta-regression using the pEC50 value as an explanatory variable. Dashed lines represent the 95% confidence interval of the regression line. The dotted lines represent the 95% prediction interval. Raw data are plotted with ‘bubble’ size adjusted according to effect size precision.

Figure 2.2.4.6 - Meta-regression of TAAR1 agonist vs control on Pre pulse inhibition by potency of the interventions

The estimate for $\beta$ was 0.51 (p = < 0.001).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	3	0
Study x Strain	4	0.13
Study x Strain x Experiment	0	NA

Dose of intervention

In this iteration of the review, the TAAR1 agonists tested against control for their effect on Pre pulse inhibition were; SEP-363856, ZH8651 and ZH8659. Meta-analysis was conducted where data were available from more than nine experiments in more than two publications, and in this iteration of the review, only SEP-363856 met that threshold.

SEP-363856 (Ultaront): There were 22 comparisons from 4 publication(s).

The estimate for $\beta$ was 0.19 (p < 0.001).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0
Study x Strain	10	0.49
Study x Strain x Experiment	20	0.42

ZH8651: There were 12 comparisons from 1 publication(s).

ZH8659: There were 12 comparisons from 1 publication(s).

Standardised dose

We then sought evidence of a dose response relationship across all drugs using the approach described for locomotor activity.

Figure 2.2.4.7 provides a visualisation of the meta-regression analysis relationship between standardised doses of TAAR1 agonists and the Standardized Mean Difference (SMD) change in Pre pulse inhibition. As before, dashed lines represent the 95% confidence interval of the regression line and dotted lines represent the 95% prediction interval. Raw data are plotted with point size adjusted according to effect size precision.

Figure 2.2.4.7 - Meta regression of standardised dose for TAAR1 agonist vs control on Pre pulse inhibition

The estimate for the change in effect per log unit change in standardised dose was 0.81 (p < 0.001).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	3	0
Study x Strain	4	0.52
Study x Strain x Experiment	0	NA

SyRCLE RoB assessment considered as a categorical variable

Figure 2.2.4.8 displays the estimates for the pooled SMD’s when comparisons are stratified by how many of the SyRCLE risk of bias assessment criteria (of which there are 10) that the experiment met. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.2.4.8 - Subgroup analysis of TAAR1 agonist vs control on Pre pulse inhibition by SyRCLE RoB criteria met

The p-value for the association between SyRCLE Risks of Bias reporting and outcome reported was = 0.328.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	0	NA
Study x Strain	0	NA
Study x Strain x Experiment	6	0.11

SyRCLE RoB assessment considering those studies where any item is at low risk of bias

Figure 2.2.4.9 displays the estimates for the pooled SMD’s when comparisons are stratified by whether of not any of the SyRCLE Risk of bias domains were rated as low risk of bias. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.2.4.9 - Subgroup analysis of TAAR1 agonist vs control on Pre pulse inhibition by alternative SyRCLE RoB assessment

The p-value for the association between low SyRCLE Risks of Bias reporting and outcome reported was = 0.188.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	0	NA
Study x Strain	0	NA
Study x Strain x Experiment	6	0.1

ARRIVE reporting completeness guidelines

Figure 2.2.4.10 displays a visualisation of the meta-regression using the number of ARRIVE items met (from a possible total of 22) as an explanatory variable. Dashed lines represent the 95% confidence interval of the regression line. The dotted lines represent the 95% prediction interval. Raw data are plotted with ‘bubble’ size adjusted according to effect size precision.

Figure 2.2.4.10 - Meta-regression of number of ARRIVE items met for TAAR1 agonist vs control on Pre pulse inhibition

The estimate for $\beta$ was 0.19 (p= 0.215).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	3	0
Study x Strain	4	0
Study x Strain x Experiment	0	NA

Heterogeneity explained by covariates (TAAR1 Agonist vs Control on Pre pulse inhibition)

Moderator	Category	$\beta$	95% CI	Marginal R² (%)
Overall effect	-	0.5	-0.05 to 1.05	-
Sex	-	-	-	30.5%
-	Female	0.7	-0.27 to 1.67	-
-	Male	0.01	-1.5 to 1.51	-
-	Mixed male and female	NA	NA to NA	-
Administration route	-	-	-	28.1%
-	Intraperitoneal	0.34	-5.13 to 5.81	-
-	Oral	0.72	-2.31 to 3.75	-
-	Subcutaneous	-0.34	-7 to 6.32	-
Intervention administered	-	-	-	35.1%
-	SEP-363856 (Ultaront)	0.37	-0.1 to 0.85	-
-	ZH8651	0.97	0.42 to 1.51	-
-	ZH8659	0.4	-0.12 to 0.93	-
Drug selectivity	-	-	-	14.3%
-	High	0.38	-0.06 to 0.83	-
-	Low	0.66	0.18 to 1.15	-
Drug potency	per log unit	0.51	0.25 to 0.77	36.2%
Standardised dose	per log unit	0.81	0.61 to 1.01	34.1%
Risk of Bias	-	-	-	44.9%
-	0 criteria met	0.06	-4.31 to 4.44	-
-	1 criteria met	0.3	-6.06 to 6.67	-
Reporting completeness	per log unit	0.19	-0.27 to 0.66	50.3%

2.2.5 Sensitivity Analyses

Imputed 𝞺 values of 0.2 and 0.8

In the previous analyses for the effect of TAAR1 agonists on Pre pulse inhibition, we imputed a $\rho$ value of 0.5. Here, we examine the effect of imputing $\rho$ values of 0.2 and 0.8.

When the $\rho$ value is assumed to be 0.2, the TAAR1 interventions had a pooled effect on Pre pulse inhibition of SMD = 0.73 (95% CI: 0.13 to 1.32) with a prediction interval of -0.66 to 2.11).

When the $\rho$ value is assumed to be 0.8, the TAAR1 interventions had a pooled effect on Pre pulse inhibition of SMD = -0.1 (95% CI: -0.94 to 0.73) with a prediction interval of -2.07 to 1.86).

For reference the pooled effect size when rho is assumed to be 0.5 is 0.5 (95% CI: -0.05 to 1.05).

Normalised Mean Difference (NMD)

For Pre pulse inhibition, 40 out of 46 comparisons, i.e. 87 % of comparisons, had data available for a Sham group, and for these studies it was possible to calculate an NMD estimate of effect size.

The effect of administering a TAAR1 agonist on Pre pulse inhibition in animals using NMD as the effect size is shown in Figure 2.2.5. The pooled estimate for NMD across all individual comparisons is displayed as a diamond shape at the bottom of the plot. Dotted lines indicate the prediction interval of the pooled estimate.

Figure 2.2.5 - Forest plot of TAAR1 agonist vs control on Pre pulse inhibition using NMD

For TAAR1 Agonist v Control, TAAR1 interventions had a pooled effect on Pre pulse inhibition of NMD = 30.4 (95% CI: -43.8 to 104.7) with a prediction interval of -141.2 to 202.1. For reference the pooled effect size for SMD was 0.5 (95% CI: -0.05 to 1.05).

40 experimental comparisons were reported in 5 experiments reported from 4 publications and involving 3 different animal strains.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	3	0
Study x Strain	4	573.2
Study x Strain x Experiment	0	NA

Robust variance estimator (RVE)

When using the robust variance estimator, TAAR1 interventions had a pooled effect on Pre pulse inhibition of SMD = 0.5 (95% CI: -1.17 to 2.17 with a prediction interval of -2.29 to 3.29). For reference the pooled effect size for SMD was 0.5 (95% CI: -0.05 to 1.05), so the using a robust variance estimator does not substantially change the results, although the confidence intervals are wider.

2.2.6 Reporting bias/small-study effects

Egger regression based on 46 effects of TAAR1 Agonist v Control where Pre pulse inhibition was measured showed a coefficient for a small study effect of 14.03 (95% CI: -16.76 to 44.82; p = 0.275).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	3	0
Study x Strain	4	0.07
Study x Strain x Experiment	0	NA

2.3 Outcome 3: Cognitive function

2.3.1 Risks of bias

Figure 2.3.1 shows the risk of bias summary for studies investigating the effect of administering a TAAR1 agonist on cognition in animals. The risk of bias assessment was performed using the SyRCLE’s RoB tool.

Figure 2.2.1 - Traffic light plot of the risk of bias for cognitive function

2.3.2 Reporting completeness

Figure 2.3.2 shows the reporting completeness summary for studies investigating the effect of administering a TAAR1 agonist on cognition in animals. The reporting completeness assessment was performed using the ARRIVE guidelines.

Figure 2.3.2 - Traffic light plot of the reporting completeness for cognitive function

2.3.3 Meta-analysis

The effect of administering a TAAR1 agonist on cognitive outcomes in animals using SMD as the effect size is shown in Figure 2.3.3. The pooled estimate for SMD across all individual comparisons is displayed as a diamond shape at the bottom of the plot. Dotted lines indicate the prediction interval of the pooled estimate.

Figure 2.3.3 - Forest plot of cognitive function for TAAR1 Agonist vs control

For TAAR1 Agonist v Control, TAAR1 interventions had a pooled effect on cognitive outcomes of SMD = 0.783 (95% CI: 0.063 to 1.504, with a prediction interval of -1 to 2.567).

34 experimental comparisons were reported in 8 experiments reported from 7 publications and involving 6 different animal strains.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0
Study x Strain	7	0.4
Study x Strain x Experiment	0	NA

2.3.4 Subgroup analyses and meta-regressions

Sex

Figure 2.3.4.1 displays the estimates for the pooled SMD’s when comparisons are stratified by sex of the animal. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.3.4.1 - Subgroup analysis of TAAR1 agonist vs control on cognitive function by sex

The p-value for the association between the sex of animal groups used and outcome reported was 0.21.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0.03
Study x Strain	7	0.19
Study x Strain x Experiment	0	NA

Category of disease induction

Figure 2.3.4.2 displays the estimates for the pooled SMD’s when comparisons are stratified by the category of disease induction. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.3.4.2 - Subgroup analysis of TAAR1 agonist vs control on cognitive function by category of disease induction

The p-value for the association between whether genetic or pharmacological models were used and outcome reported was 0.16.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0
Study x Strain	7	0.27
Study x Strain x Experiment	0	NA

Route of intervention administration

Figure 2.3.4.3 displays the estimates for the pooled SMD’s when comparisons are stratified by the administration route of the intervention. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.3.4.3 - Subgroup analysis of TAAR1 agonist vs control on cognitive function by route of intervention administration

The p-value for the association between whether genetic or pharmacological models were used and outcome reported was 0.12.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0
Study x Strain	7	0.22
Study x Strain x Experiment	0	NA

Prophylactic or therapeutic intervention

In this iteration of the review, all relevant comparisons administered the TAAR1 agonist after induction of the disease model. Therefore, no subgroup analyses were conducted for this variable.

Duration of treatment period

In this iteration of the review, all relevant comparisons administered the TAAR1 agonist for < 1 week. Therefore, no subgroup analyses were conducted for this variable.

The intervention administered

Figure 2.3.4.4 displays the estimates for the pooled SMD’s when comparisons are stratified by the intervention administered. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.3.4.4 - Subgroup analysis of TAAR1 agonist vs control on cognitive function by intervention administered

The p-value for the association between the intervention and outcome reported was 0.57.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0
Study x Strain	7	0.52
Study x Strain x Experiment	0	NA

The efficacy of the drug (i.e. whether the drug is a partial or full agonist)

In this iteration of the review, all relevant comparisons administered the TAAR1 agonists with partial agonist activity. Therefore, no subgroup analyses were conducted for this variable.

The selectivity of the drug

Figure 2.3.4.5 displays the estimates for the pooled SMD’s when comparisons are stratified by the selectivity of the intervention administered. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.3.4.5 - Subgroup analysis of TAAR1 agonist vs control on cognitive function by selectivity of the drug

The p-value for the association between whether the drug was highly selective, or also manifests 5-HT1A effects, was 0.08.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0.07
Study x Strain	7	0.42
Study x Strain x Experiment	0	NA

Potency of interventions

The pEC50 value of each drug was used to measure potency. The pEC50 value is the negative logarithm (to base 10) of the EC50 value. Higher pEC50 values indicate higher potency (as they indicate a lower EC50). Figure 2.3.4.6 displays a visualisation of the meta-regression using the pEC50 value as an explanatory variable. Dashed lines represent the 95% confidence interval of the regression line. The dotted lines represent the 95% prediction interval. Raw data are plotted with ‘bubble’ size adjusted according to effect size precision.

Figure 2.3.4.6 - Meta-regression of TAAR1 agonist vs control on cognitive function by potency of the interventions

The estimate for $\beta$ was -0.54 (p = 0.04).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0
Study x Strain	7	0.51
Study x Strain x Experiment	0	NA

Dose of intervention

In this iteration of the review, the TAAR1 agonists tested against control for their effect on cognition were; SEP-363856, RO5256390, RO5203648, Compound 6e, Compound 7b, Compound 8b, ZH8651 and ZH8659. Meta-analysis was conducted where data were available from more than nine experiments in more than two publications, and in this iteration of the review only SEP-363856 met this threshold.

SEP-363856 (Ultaront): There were 24 comparisons from 5 publication(s).

The estimate for $\beta$ was 0.14 (p = < 0.001).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	4	0
Study x Strain	5	0.15
Study x Strain x Experiment	6	0

RO5203648: There were 3 comparisons from 1 publication(s).

RO5203648: There were 2 comparisons from 1 publication(s).

RO5263397: There were 1 comparisons from 1 publication(s).

RO5166017: There were 1 comparisons from 1 publication(s).

LK000764: There were 1 comparisons from 1 publication(s).

RO5256390: There were 1 comparisons from 1 publication(s).

Compound 50B: There were 1 comparisons from 1 publication(s).

Standardised dose

We then sought evidence of a dose response relationship across all drugs using the approach described for locomotor activity.

Figure 2.3.4.7 provides a visualisation of the meta-regression analysis relationship between standardised doses of TAAR1 agonists and the Standardized Mean Difference (SMD) change in cognition. As before, dashed lines represent the 95% confidence interval of the regression line and dotted lines represent the 95% prediction interval. Raw data are plotted with point size adjusted according to effect size precision.

Figure 2.3.4.7 - Meta regression of standardised dose for TAAR1 agonist vs control on cognitive function

The estimate for the change in effect per log unit change in standardised dose was 0.36 (p = 0.012).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0
Study x Strain	7	0.4
Study x Strain x Experiment	0	NA

SyRCLE RoB assessment considered as a categorical variable

Figure 2.3.4.8 displays the estimates for the pooled SMD’s when comparisons are stratified by how many of the SyRCLE risk of bias assessment criteria (of which there are 10) that the experiment met. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.3.4.8 - Subgroup analysis of TAAR1 agonist vs control on cognitive function by SyRCLE RoB criteria met

The p-value for the association between SyRCLE Risks of Bias reporting and outcome reported was 0.3.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0.18
Study x Strain	7	0.18
Study x Strain x Experiment	0	NA

SyRCLE RoB assessment considering those studies where any item is at low risk of bias

Figure 2.3.4.9 displays the estimates for the pooled SMD’s when comparisons are stratified by whether of not any of the SyRCLE Risk of bias domains were rated as low risk of bias. Whiskers indicate the 95% confidence interval of each estimate. The overall pooled SMD is displayed as a diamond shape at the bottom of the plot.

Figure 2.3.4.9 - Subgroup analysis of TAAR1 agonist vs control on cognitive function by alternative SyRCLE RoB assessment

The p-value for the association between low SyRCLE Risks of Bias reporting and outcome reported was 0.13.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0.09
Study x Strain	7	0.17
Study x Strain x Experiment	0	NA

ARRIVE reporting completeness guidelines

Figure 2.3.4.10 displays a visualisation of the meta-regression using the number of ARRIVE items met (from a possible total of 22) as an explanatory variable. Dashed lines represent the 95% confidence interval of the regression line. The dotted lines represent the 95% prediction interval. Raw data are plotted with ‘bubble’ size adjusted according to effect size precision.

Figure 2.3.4.10 - Meta-regression of number of ARRIVE items met for TAAR1 agonist vs control on cognitive function

The estimate for $\beta$ was 0.05 (p = 0.78).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0
Study x Strain	7	0.53
Study x Strain x Experiment	0	NA

Heterogeneity explained by covariates (TAAR1 Agonist vs Control on cognitive function)

Moderator	Category	$\beta$	95% CI	Marginal R² (%)
Overall effect	-	0.78	0.06 to 1.5	-
Sex	-	-	-	43.5%
-	Female	2.28	0.1 to 4.45	-
-	Male	0.56	-0.3 to 1.42	-
-	Mixed male and female	0.65	-1.07 to 2.38	-
Category of disease model induction	-	-	-	24.6%
-	Genetic	-0.31	-2.19 to 1.58	-
-	Pharmacological	0.93	0.21 to 1.66	-
Administration route	-	-	-	48.5%
-	Intraperitoneal	0.07	-1.1 to 1.24	-
-	Oral	1.06	0.3 to 1.82	-
Intervention administered	-	-	-	23.5%
-	Compound 6e	1.03	-0.1 to 2.16	-
-	Compound 7b	0.49	-0.62 to 1.6	-
-	Compound 8b	0.34	-0.77 to 1.44	-
-	RO5203648	-0.31	-10.99 to 10.37	-
-	RO5256390	0.85	-9.77 to 11.47	-
-	SEP-363856 (Ultaront)	1.16	0.4 to 1.92	-
-	ZH8651	0.86	-0.27 to 1.99	-
-	ZH8659	0.35	-0.75 to 1.45	-
Drug selectivity	-	-	-	19.2%
-	High	0.28	-1.58 to 2.13	-
-	Low	1.14	0.39 to 1.9	-
Drug potency	per log unit	-0.54	-1.06 to -0.02	8.9%
Standardised dose	per log unit	0.36	0.09 to 0.64	13.2%
Risk of Bias	-	-	-	38.1%
-	0 criteria met	0.4	-0.7 to 1.51	-
-	1 criteria met	1.29	-0.15 to 2.73	-
Reporting completeness	per log unit	0.05	-0.36 to 0.46	1.7%

2.3.5 Sensitivity Analyses

Imputed 𝞺 values of 0.2 and 0.8

In the previous analyses for the effect of TAAR1 agonists on cognition, we imputed a $\rho$ value of 0.5. Here, we examine the effect of imputing $\rho$ values of 0.2 and 0.8.

When the $\rho$ value is assumed to be 0.2, the TAAR1 interventions had a pooled effect on cognition of SMD = 0.92 (95% CI: 0.21 to 1.62) with a prediction interval of -0.9 to 2.74).

When the $\rho$ value is assumed to be 0.8, the TAAR1 interventions had a pooled effect on cognition of SMD = 0.38 (95% CI: -0.8 to 1.56) with a prediction interval of -2.57 to 3.33).

For reference the pooled effect size when rho is assumed to be 0.5 is 0.78 (95% CI: 0.06 to 1.5).

Normalised Mean Difference (NMD)

For cognition, 34 out of 34 comparisons, i.e. 100 % of comparisons, had data available for a Sham group, and for these studies it was possible to calculate an NMD estimate of effect size.

The effect of administering a TAAR1 agonist on cognition in animals using NMD as the effect size is shown in Figure 2.2.5. The pooled estimate for NMD across all individual comparisons is displayed as a diamond shape at the bottom of the plot. Dotted lines indicate the prediction interval of the pooled estimate.

Figure 2.3.5 - Forest plot of TAAR1 agonist vs control on cognitive function using NMD

For TAAR1 Agonist v Control, TAAR1 interventions had a pooled effect on cognition of NMD = 47.2 (95% CI: 1 to 93.4) with a prediction interval of -75.5 to 169.9. For reference the pooled effect size for SMD was 0.78 (95% CI: 0.06 to 1.5).

34 experimental comparisons were reported in 8 experiments reported from 7 publications and involving 6 different animal strains.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	1669.02
Study x Strain	7	280.33
Study x Strain x Experiment	0	NA

Robust variance estimator (RVE)

When using the robust variance estimator, TAAR1 interventions had a pooled effect on cognition of SMD = 0.78 (95% CI: 0.08 to 1.48 with a prediction interval of -1.05 to 2.62). For reference the pooled effect size for SMD was 0.78 (95% CI: 0.06 to 1.5), so the using a robust variance estimator does not substantially change the results.

2.3.6 Reporting bias/small-study effects

Egger regression based on 34 effects of TAAR1 Agonist v Control where Cognitive function was measured showed a coefficient for a small study effect of -5.09 (95% CI: -37.37 to 27.2; p = 0.702).

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	6	0
Study x Strain	7	0.53
Study x Strain x Experiment	0	NA

3 TAAR1 Agonist v known antipsychotic drug

3.1 Outcome 1: Locomotor activity

In TAAR1 Agonist v known antipsychotic drug studies, the effect of administering a TAAR1 agonist on Locomotor activity in animals using SMD as the effect size is shown in Figure 3.1. The pooled estimate for SMD across all individual comparisons is displayed as a diamond shape at the bottom of the plot. Dotted lines indicate the prediction interval of the pooled estimate.

Figure 3.1 - Forest plot of Locomotor activity for TAAR1 Agonist vs known antipychotic drug

For TAAR1 Agonist v known antipsychotic drug comparisons, TAAR1 interventions had a pooled effect on locomotor activity of SMD =-0.801 (95% CI: -1.763 to 0.16, with a prediction interval of-2.877 to 1.274).

27 experimental comparisons were reported in 8 experiments reported from 5 publications and involving 3 different animal strains.

Level	Number of categories for that level included in this analysis	Attributable variance
Strain	0	NA
Study x Strain	0	NA
Study x Strain x Experiment	0	NA

3.2 Outcome 2: Pre pulse inhibition

Only one study reported pre pulse inhibition in this category, so meta-analysis was not performed.

3.3 Outcome 3: Cognitive function

Only two studies reported cognitive outcomes in this category, so meta-analysis was not performed.

4 Co-treatment with TAAR1 agonist plus known antipsychotic drug v known antipsychotic drug alone

4.1 Outcome 1: Locomotor activity

Multilevel analysis is only performed if there are 5 levels or more for at least one of Strain, Study and Experiment, and that is not the case here. We provide a conventional univariate random effects model to illustrate the data

4.2 Outcome 2: Pre pulse inhibition

No studies reported pre pulse inhibition in this category, so meta-analysis was not performed.

4.3 Outcome 3: Cognitive function

Only one study reported cognitive outcomes in this category, so meta-analysis was not performed.

5 Effect of TAAR1 agonists in TAAR1 receptor knockout animals

5.1 Outcome 1: Locomotor activity

The effect on locomotor activity of administering a TAAR1 agonist in transgenic animals lacking the gene for the TAAR1 receptor is shown in Figure 5.1. The pooled estimate for SMD across all individual comparisons is displayed as a diamond shape at the bottom of the plot. Dotted lines indicate the prediction interval of the pooled estimate.

Figure 5.1 - Forest plot of Locomotor activity for TAAR1 Agonists in TAAR1 receptor knockout animals

5.2 Outcome 2: Pre pulse inhibition

Only one study reported pre pulse inhibition in TAAR1 knockout animals, so meta-analysis was not performed.

5.3 Outcome 3: Cognitive function

No studies reported cognitive outcomes in TAAR1 knockout animals

6. Proportion of animals not progressing to outcome measurement, potentially reflecting adverse effects of treatment

6.1% of 1577 animals in Control cohorts and 11.9% of 1577 animals in Intervention cohorts ‘dropped out’ between allocation to group and outcome measurement. Given that 307 of 392 interventions (78.3%) were administered as a single dose, treatment emergent adverse effects likely to lead to withdrawal of an animal from the study would be unusual, and technical failure or attrition is more likely. This analysis is based on full reporting of animals excluded from analyses, and it may be that group sizes were specified ‘after the event’, or that there was unreported replacement of animals excluded during the experiment, so these data should be interpreted with considerable caution.

7. Summary of the evidence

7.1 TAAR1 agonists versus control

Outcome	Summary of the association	Within-study biases	Across-studies biases	Indirectness	Other biases
Locomotor activity	188 experimental comparisons from 60 experiments in 21 publications involving 11 animal strains; SMD = 1.109 (95% CI: 0.837 to 1.38; 95% PrI -0.507 to 2.724) (Section 2.1.3). Some heterogeneity was observed. For pharmacological disease models, effects were larger for NMDA antagonist modesl than for dopaminergic/ stimulant models (Section 2.1.4.3). Drug effects: there was no significant modifying effect of drug selectivity or potency (Section 2.1.4) but there was a dose response relationship for RO5263397 and SEP-363856 (Ultaront) and for standardised dose (Fig 2.1.4.11)	Moderate risk of bias likely to exaggerate the effects of TAAR1 agonists. All studies had unclear risk of bias for most of the SyRCLE items. Reporting was mostly incomplete; the median number of ARRIVE items reported was 12 (of 22).	Moderate risk of bias likely to exaggerate the effects of TAAR1 agonists. No studies preregistered their analyses. There was evidence of small-study effects (Section 2.1.6).	Moderate risk of indirectness. For explanation, see [1] below.	No other risks identified.
Pre pulse inhibition	46 experimental comparisons from 6 experiments in 4 publications involving 3 animal strains; SMD = 0.498 (95% CI: -0.051 to 1.048; 95% PrI -0.625 to 1.622) (Section 2.2.3). No significant heterogeneity was observed. Drug effects: there was a significant inverse effect of drug potency, dose of SEP-363856 and standardised dose but no significant modifying effect of drug or drug selectivity (Section 2.3.4).	Moderate risk of bias likely to exaggerate the effects of TAAR1 agonists. All studies had unclear risk of bias for most of the SyRCLE items. Reporting was mostly incomplete; the median number of ARRIVE items reported was 12 (of 22).	Moderate risk of bias likely to exaggerate the effects of TAAR1 agonists. No studies preregistered their analyses. There was no evidence of small-study effects (Section 2.2.6).	Moderate risk of indirectness. For explanation, see [2] below.	No other risks identified.
Cognition	34 experimental comparisons from 8 experiments in 7 publications involving 6 animal strains; SMD = 0.783 (95% CI: 0.063 to 1.504; 95% PrI -1.000 to 2.567) (Section 2.3.3). No significant heterogeneity was observed. Drug effects: there was a significant inverse effect of drug potency, and significant direct effects of dose of SEP-363856 and standardised dose but no significant modifying effect of drug or drug selectivity (Section 2.3.4).	Moderate risk of bias likely to exaggerate the effects of TAAR1 agonists. All studies had unclear risk of bias for most of the SyRCLE items. Reporting was mostly incomplete; the median number of ARRIVE items reported was 15 (of 22).	Moderate risk of bias likely to exaggerate the effects of TAAR1 agonists. No studies preregistered their analyses. There was no evidence of small-study effects (Section 2.3.6).	Moderate risk of indirectness. For explanation, see [3] below.	No other risks identified.

7.2 TAAR1 agonists versus conventional antipsychotic drugs

Outcome	Summary of the association	Within-study biases	Across-studies biases	Indirectness	Other biases
Locomotor activity	27 experimental comparisons from 8 experiments in 5 publications involving 3 animal strains; SMD = -0.801 (95% CI: -1.763 to 0.16; 95% PrI -2.272 to 1.029). Sources of heterogeneity were not evaluated	Moderate risk of bias likely to exaggerate the effects of TAAR1 agonists. All studies had unclear risk of bias for most of the SyRCLE items. Reporting was mostly incomplete; the median number of ARRIVE items reported was 12 (of 22).	Moderate risk of bias likely to exaggerate the effects of TAAR1 agonists. No studies preregistered their analyses. Evidence for small-study effects not saught.	Moderate risk of indirectness. For explanation, see [4] below.	No other risks identified.
Pre pulse inhibition	6 experimental comparisons from 1 experiment in 1 publication involving 1 animal strain; insufficient data for further analysis.	The included study was at unclear risk of bias (SyRCLE, all items); the median number of ARRIVE items reported was 12 (of 22).	Moderate risk of bias likely to exaggerate the effects of TAAR1 agonists. The study did not preregister its analyses.	Moderate risk of indirectness. For explanation, see [5] below.	No other risks identified.
Cognition	11 experimental comparisons from 2 experiment in 2 publications involving 2 animal strains; insufficient data for further analysis.	The included studies were at unclear risk of bias (SyRCLE, all items); the median number of ARRIVE items reported was 14 (of 22).	Moderate risk of bias likely to exaggerate the effects of TAAR1 agonists. The study did not preregister its analyses.	Moderate risk of indirectness. For explanation, see [6] below.	No other risks identified.

Rationale for conclusions for indirectness: [1] TAARI 1 agonists v control, outcome ‘Locomotor activity’: Moderate risk of indirectness We had concerns for indirectness because all experiments were in rodents; no models manipulated early environmental factors; and psychomotor agitation is not identified by the JLA schizophrenia Priority Setting Partnership ‘Top 10’. Further, in rat brain slices, TAAR1 antagonists inhibit met-amphetamine induced- but not basal- dopamine release; and SEP-363856 (Ulotaront) inhibits ketamine-induced striatal dopamine synthesis in the mouse, suggesting that some of the effects of TAAR1 agonism may be due to interference with model induction rather than reversal of the induced phenotype.

However, for models using DAT knock out, the homologous human gene is associated with schizophrenia in some populations, indirect DAT inhibitors can cause psychosis in humans, and the effect of indirect DAT inhibitors is reported to be mediated through TAAR1 agonism. For the pharmacological models used to induce locomotor activity the same agents used in animal models induce psychosis and exacerbate symptoms in humans and induce EEG changes in humans and animals which are responsive to treatment in animals. Psychostimulant models induce mesolimbic dopamine dysregulation seen in humans, and the PCP model is associated with reduced brain volume, also seen in human disease.

[2] TAARI 1 agonists v control, outcome ‘Prepulse inhibition’: Moderate risk of indirectness We had concerns for indirectness because all experiments were in rodents; no models manipulated early environmental factors; and impaired prepulse inhibition is not identified by the JLA schizophrenia Priority Setting Partnership ‘Top 10’. For the pharmacological models used to induce locomotor activity the same agents used in animal models induce psychosis and exacerbate symptoms in humans and induce EEG changes in humans and animals which are responsive to treatment in animals. Psychostimulant models induce mesolimbic dopamine dysregulation seen in humans.

[3] TAARI 1 agonists v control, outcome ‘Cognitive outcomes’: Moderate risk of indirectness We had concerns for indirectness because all experiments were in rodents; no models manipulated early environmental factors; and impaired cognition is not identified by the JLA schizophrenia Priority Setting Partnership ‘Top 10’. However, for models using DAT knock out, the homologous human gene is associated with schizophrenia in some populations, indirect DAT inhibitors can cause psychosis in humans, and the effect of indirect DAT inhibitors is reported to be mediated through TAAR1 agonism. For the pharmacological models used to induce locomotor activity the same agents used in animal models induce psychosis and exacerbate symptoms in humans and induce EEG changes in humans and animals which are responsive to treatment in animals. Psychostimulant models induce mesolimbic dopamine dysregulation seen in humans, and the PCP model is associated with reduced brain volume, also seen in human disease.

[4] TAARI 1 agonists v conventional antipsychotic drugs, outcome ‘Locomotor activity’: Moderate risk of indirectness We had concerns for indirectness because all experiments were in rodents; no models manipulated early environmental factors; and psychomotor agitation identified by the JLA schizophrenia Priority Setting Partnership ‘Top 10’. For the pharmacological models used to induce locomotor activity the same agents used in animal models induce psychosis and exacerbate symptoms in humans and induce EEG changes in humans and animals which are responsive to treatment in animals. Psychostimulant models induce mesolimbic dopamine dysregulation seen in humans, and the PCP model is associated with reduced brain volume, also seen in human disease.

[5] TAARI 1 agonists v conventional antipsychotic drugs, outcome ‘Prepulse inhibition’: Moderate risk of indirectness Only one publication contributes to this outcome.

[6] TAARI 1 agonists v conventional antipsychotic drugs, outcome ‘Cognitive outcomes’: Moderate risk of indirectness Only two publications contribute to this outcome.

Evaluation of indirectness of evidence (based on criteria in document “Assessing the certainty of evidence in animal studies”) for the studies included in the review

The framework for the evaluation of indirectness is based on eight dimensions, based on the work of Belzung and Lemoine, and comprising (i) Homological validity - what is the extent of homology between the model organism and humans relevant to the condition studied? (ii) Ontopathogenic validity - Does the model include prenatal or early life exposures inducing transition from initial organism to vulnerable organism? (iii) Triggering validity - are any triggering factors used in the modelling – or their homologues - known to induce psychosis or relapse in humans? (iv) Mechanistic validity - whether the neurobiological or cognitive mechanisms which operate in human disease can be observed in the animal model; (v) Induction validity - Does the induction of the disease model induce changes in biomarkers (see below) which are known to be altered in human disease? (vi) Remission validity - What is the effect of other drugs known to be effective in humans in the particular animal model / outcome measure pair? (vii) Biomarker validity - are changes in disease markers (e.g. neurotransmitter levels, structural brain imaging) seen in human disease also seen in this animal model? (viii) Ethological validity - what is the ‘behavioural distance’ between the model phenotype in animals and the symptoms and signs of human disease at which treatment is targeted?

Dimension	Characteristic	Homological validity	Ontopathogenic validity	Triggering validity	Mechanistic validity	Induction validity	Remission validity	Biomarker validity	Ethological validity
Species and strain	Rat, Mouse	We could find no evidence that the rat behavioural repertoire is closer to human than is the mouse	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.	n.a.
Model Induction	Models using genetic induction – the DAT KO model	Polymorphisms in human SLC6A3 (DAT) gene reportedly associated with schizophrenia in some populations	No	Indirect DAT inhibitors such as methamphetamine can induce psychosis in humans.	The effect of indirect DAT inhibitors is thought to be mediated through TAAR1 agonism	n.a.	n.a.	n.a.	n.a.
~	Pharmacological models (psychostimulant models (cocaine, amphetamine etc), NMDA models (phencyclidine, MK801 etc))	n.a.	No	MK801, ketamine, PCP and amphetamine induce psychosis and exacerbate symptoms in humans	Psychostimulant models induce mesolimbic dopamine dysregulation	1.The chronic PCP model has been associated with reduced brain volume; 2.EEG changes induced by amphetamine, PCP and MK801 are seen in human disease	In vivo EEG changes induced by amphetamine, PCP and MK801 are responsive to treatment	The chronic PCP model has been associated with reduced brain volume; 2. EEG changes induced by amphetamine, PCP and MK801 are seen in human disease	n.a.
Outcome Measure	Locomotor activity	n.a.	n.a.	n.a.	n.a.	n.a.	In a systematic review, Bahor found that known antipsychotic drugs improved locomotor activity in developmental models of psychosis. In house data from a Masters project (2015) suggests that some (clozapine, aripiprazole, fluphenazine) but not all (eg olanzapine) improve cocaine induced locomotor activity.	n.a.	Psychomotor agitation, prepulse inhibition and Cognitive impairment are not listed on the JLA schizophrenia PSP top 10, and so the ethological validity of these measures as relevant to unmet clinical need is uncertain.
~	Prepulse inhibition	n.a.	n.a.	n.a.	n.a.	n.a.	We could find no SRs of the effects of known antipsychotic drugs.	n.a.	NA
~	Cognition	n.a.	n.a.	n.a.	n.a.	n.a.	We could find no SRs of the effects of known antipsychotic drugs.	n.a.	NA
Additional experimental contrasts	TAAR1 agonists v conventional antipsychotics	n.a.	n.a.	n.a.	n.a.	n.a.	In head-to-head experiments, efficacy is non significantly lower than conventional antipsychotics	n.a.	Relevant to potential use as monotherapy

The description of the criteria is available at https://doi.org/10.17605/OSF.IO/TDMAU

8. Software used

We used R v. 4.5.1 (R Core Team 2025) and the following R packages: clubSandwich v. 0.6.2.9999 (Pustejovsky 2026), devtools v. 2.4.5 (Wickham et al. 2022), dosresmeta v. 2.2.0 (Crippa and Orsini 2016), gtools v. 3.9.5 (Warnes et al. 2023), Hmisc v. 5.2.5 (Harrell Jr 2026), kableExtra v. 1.4.0 (Zhu 2024), knitr v. 1.50 (Xie 2014, 2015, 2025), Matrix v. 1.7.3 (Bates, Maechler, and Jagan 2025), meta v. 8.1.0 (Balduzzi, Rücker, and Schwarzer 2019), metadat v. 1.4.0 (Viechtbauer et al. 2025), metafor v. 4.8.0 (Viechtbauer 2010), mixmeta v. 1.2.2 (F. Sera et al. 2019), numDeriv v. 2016.8.1.1 (Gilbert and Varadhan 2019), orchaRd v. 2.1.3 (Nakagawa et al. 2023), patchwork v. 1.3.2 (Pedersen 2025), PRISMA2020 v. 1.1.1 (Haddaway et al. 2022), rje v. 1.12.1 (Evans 2022), rms v. 8.1.0 (Harrell Jr 2025), robvis v. 0.3.0.900 (McGuinness and Higgins 2020), tidyverse v. 2.0.0 (Wickham et al. 2019), usethis v. 3.1.0 (Wickham et al. 2024), xtable v. 1.8.4 (Dahl et al. 2019).

Balduzzi, Sara, Gerta Rücker, and Guido Schwarzer. 2019. “How to Perform a Meta-Analysis with R: A Practical Tutorial.” Evidence-Based Mental Health, no. 22: 153–60.

Bates, Douglas, Martin Maechler, and Mikael Jagan. 2025. Matrix: Sparse and Dense Matrix Classes and Methods. https://doi.org/10.32614/CRAN.package.Matrix.

Crippa, Alessio, and Nicola Orsini. 2016. “Multivariate Dose-Response Meta-Analysis: The dosresmeta R Package.” Journal of Statistical Software, Code Snippets 72 (1): 1–15. https://doi.org/10.18637/jss.v072.c01.

Dahl, David B., David Scott, Charles Roosen, Arni Magnusson, and Jonathan Swinton. 2019. xtable: Export Tables to LaTeX or HTML. https://doi.org/10.32614/CRAN.package.xtable.

Evans, Robin. 2022. rje: Miscellaneous Useful Functions for Statistics. https://doi.org/10.32614/CRAN.package.rje.

F. Sera, B. Armstrong, M. Blangiardo, and A. Gasparrini. 2019. “An Extended Mixed-Effects Framework for Meta-Analysis.” Statistics in Medicine 38 (29): 5429–44. https://doi.org/10.1002/sim.8362.

Gilbert, Paul, and Ravi Varadhan. 2019. numDeriv: Accurate Numerical Derivatives. https://doi.org/10.32614/CRAN.package.numDeriv.

Haddaway, Neal R, Matthew J Page, Chris C Pritchard, and Luke A McGuinness. 2022. “PRISMA2020: An r Package and Shiny App for Producing PRISMA 2020-Compliant Flow Diagrams, with Interactivity for Optimised Digital Transparency and Open Synthesis.” Campbell Systematic Reviews 18 (2): e1230. https://doi.org/10.1002/cl2.1230.

Harrell Jr, Frank E. 2025. rms: Regression Modeling Strategies. https://doi.org/10.32614/CRAN.package.rms.

———. 2026. Hmisc: Harrell Miscellaneous. https://doi.org/10.32614/CRAN.package.Hmisc.

McGuinness, Luke A, and Julian PT Higgins. 2020. “Risk-of-Bias VISualization (Robvis): An r Package and Shiny Web App for Visualizing Risk-of-Bias Assessments.” Research Synthesis Methods. https://doi.org/10.1002/jrsm.1411.

Nakagawa, Shinichi, Malgorzata Lagisz, Rose E. O’Dea, Patrice Pottier, Joanna Rutkowska, Alistair M. Senior, Yefeng Yang, and Daniel W. A. Noble. 2023. “orchaRd 2.0: An r Package for Visualizing Meta-Analyses with Orchard Plots.” EcoEvoRxiv 12: 4–12. https://doi.org/https://doi.org/10.32942/X2QC7K.

Pedersen, Thomas Lin. 2025. patchwork: The Composer of Plots. https://doi.org/10.32614/CRAN.package.patchwork.

Pustejovsky, James E. 2026. clubSandwich: Cluster-Robust (Sandwich) Variance Estimators with Small-Sample Corrections. https://github.com/jepusto/clubSandwich.

R Core Team. 2025. R: A Language and Environment for Statistical Computing. Vienna, Austria: R Foundation for Statistical Computing. https://www.R-project.org/.

Viechtbauer, Wolfgang. 2010. “Conducting Meta-Analyses in R with the metafor Package.” Journal of Statistical Software 36 (3): 1–48. https://doi.org/10.18637/jss.v036.i03.

Viechtbauer, Wolfgang, Thomas White, Daniel Noble, Alistair Senior, and W. Kyle Hamilton. 2025. metadat: Meta-Analysis Datasets. https://doi.org/10.32614/CRAN.package.metadat.

Warnes, Gregory R., Ben Bolker, Thomas Lumley, Arni Magnusson, Bill Venables, Genei Ryodan, and Steffen Moeller. 2023. gtools: Various r Programming Tools. https://doi.org/10.32614/CRAN.package.gtools.

Wickham, Hadley, Mara Averick, Jennifer Bryan, Winston Chang, Lucy D’Agostino McGowan, Romain François, Garrett Grolemund, et al. 2019. “Welcome to the tidyverse.” Journal of Open Source Software 4 (43): 1686. https://doi.org/10.21105/joss.01686.

Wickham, Hadley, Jennifer Bryan, Malcolm Barrett, and Andy Teucher. 2024. usethis: Automate Package and Project Setup. https://doi.org/10.32614/CRAN.package.usethis.

Wickham, Hadley, Jim Hester, Winston Chang, and Jennifer Bryan. 2022. devtools: Tools to Make Developing r Packages Easier. https://doi.org/10.32614/CRAN.package.devtools.

Xie, Yihui. 2014. “knitr: A Comprehensive Tool for Reproducible Research in R.” In Implementing Reproducible Computational Research, edited by Victoria Stodden, Friedrich Leisch, and Roger D. Peng. Chapman; Hall/CRC.

———. 2015. Dynamic Documents with R and Knitr. 2nd ed. Boca Raton, Florida: Chapman; Hall/CRC. https://yihui.org/knitr/.

———. 2025. knitr: A General-Purpose Package for Dynamic Report Generation in R. https://yihui.org/knitr/.

Zhu, Hao. 2024. kableExtra: Construct Complex Table with “kable” and Pipe Syntax. https://doi.org/10.32614/CRAN.package.kableExtra.

LSR3 analysis: effects of TAAR1 agonists in animal models of psychosis

Francesca Tinsdeall, Fiona Ramage, Virginia Chiocchia, Spyridon Siafis and Malcolm Macleod

02 February 2026

1. Flow of study selection and descriptives

1.1 Description of experiment types and methodological approach

2. TAAR1 Agonists v Control

2.1 Outcome 1: Locomotor Activity

2.1.1 Risks of bias

2.1.2 Reporting completeness

2.1.3 Meta-analysis

2.1.4 Subgroup analyses and meta-regressions

Sex

Category of disease induction

Disease model induction

Route of intervention administration

Prophylactic or therapeutic intervention

Duration of treatment period

The intervention administered

The efficacy of the drug (i.e. whether the drug is a partial or full agonist)

The selectivity of the drug

Potency of intervention

Dose of intervention

Standardised dose

SyRCLE RoB assessment considered as a categorical variable

SyRCLE RoB assessment considering those studies where any item is at low risk of bias

ARRIVE reporting completeness guidelines

Heterogeneity explained by covariates (TAAR1 Agonist vs Control on locomotor activity)

2.1.5 Sensitivity Analyses

Imputed 𝞺 values of 0.2 and 0.8

Normalised Mean Difference (NMD)

Robust variance estimator (RVE)

2.1.6 Reporting bias/small-study effects

2.2 Outcome 2: Pre pulse inhibition

2.2.1 Risks of bias

2.2.2 Reporting completeness

2.2.3 Meta-analysis

2.2.4 Subgroup analyses and meta-regressions

Sex

Category of disease induction

Disease model induction

Route of intervention administration

Prophylactic or therapeutic intervention

Duration of treatment period

The intervention administered

The efficacy of the drug (i.e. whether the drug is a partial or full agonist)

The selectivity of the drug

Potency of interventions

Dose of intervention

Standardised dose

SyRCLE RoB assessment considered as a categorical variable

SyRCLE RoB assessment considering those studies where any item is at low risk of bias

ARRIVE reporting completeness guidelines

Heterogeneity explained by covariates (TAAR1 Agonist vs Control on Pre pulse inhibition)

2.2.5 Sensitivity Analyses

Imputed 𝞺 values of 0.2 and 0.8

Normalised Mean Difference (NMD)

Robust variance estimator (RVE)

2.2.6 Reporting bias/small-study effects

2.3 Outcome 3: Cognitive function

2.3.1 Risks of bias

2.3.2 Reporting completeness

2.3.3 Meta-analysis

2.3.4 Subgroup analyses and meta-regressions

Sex

Category of disease induction

Route of intervention administration

Prophylactic or therapeutic intervention

Duration of treatment period

The intervention administered

The efficacy of the drug (i.e. whether the drug is a partial or full agonist)

The selectivity of the drug

Potency of interventions

Dose of intervention

Standardised dose

SyRCLE RoB assessment considered as a categorical variable

SyRCLE RoB assessment considering those studies where any item is at low risk of bias

ARRIVE reporting completeness guidelines

Heterogeneity explained by covariates (TAAR1 Agonist vs Control on cognitive function)

2.3.5 Sensitivity Analyses

Imputed 𝞺 values of 0.2 and 0.8